Imported WebKit commit 2ea9d364d0f6efa8fa64acf19f451504c59be0e4 (http://svn.webkit.org/repository/webkit/trunk@104285)

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diff --git a/Source/JavaScriptCore/heap/DFGCodeBlocks.h b/Source/JavaScriptCore/heap/DFGCodeBlocks.h
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+/*
+ * Copyright (C) 2011 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef DFGCodeBlocks_h
+#define DFGCodeBlocks_h
+
+#include <wtf/FastAllocBase.h>
+#include <wtf/HashSet.h>
+#include <wtf/PassOwnPtr.h>
+
+namespace JSC {
+
+class CodeBlock;
+class SlotVisitor;
+
+// DFGCodeBlocks notifies the garbage collector about optimized code blocks that
+// have different marking behavior depending on whether or not they are on the
+// stack, and that may be jettisoned. Jettisoning is the process of discarding
+// a code block after all calls to it have been unlinked. This class takes special
+// care to ensure that if there are still call frames that are using the code
+// block, then it should not be immediately deleted, but rather, it should be
+// deleted once we know that there are no longer any references to it from any
+// call frames. This class takes its name from the DFG compiler; only code blocks
+// compiled by the DFG need special marking behavior if they are on the stack, and
+// only those code blocks may be jettisoned.
+
+#if ENABLE(DFG_JIT)
+class DFGCodeBlocks {
+    WTF_MAKE_FAST_ALLOCATED;
+
+public:
+    DFGCodeBlocks();
+    ~DFGCodeBlocks();
+    
+    // Inform the collector that a code block has been jettisoned form its
+    // executable and should only be kept alive if there are call frames that use
+    // it. This is typically called either from a recompilation trigger, or from
+    // an unconditional finalizer associated with a CodeBlock that had weak
+    // references, where some subset of those references were dead.
+    void jettison(PassOwnPtr<CodeBlock>);
+    
+    // Clear all mark bits associated with DFG code blocks.
+    void clearMarks();
+    
+    // Mark a pointer that may be a CodeBlock that belongs to the set of DFG code
+    // blocks. This is defined inline in CodeBlock.h
+    void mark(void* candidateCodeBlock);
+    
+    // Delete all jettisoned code blocks that have not been marked (i.e. are not referenced
+    // from call frames).
+    void deleteUnmarkedJettisonedCodeBlocks();
+    
+    // Trace all marked code blocks (i.e. are referenced from call frames). The CodeBlock
+    // is free to make use of m_dfgData->isMarked and m_dfgData->isJettisoned.
+    void traceMarkedCodeBlocks(SlotVisitor&);
+
+private:
+    friend class CodeBlock;
+    
+    HashSet<CodeBlock*> m_set;
+};
+#else
+class DFGCodeBlocks {
+    WTF_MAKE_FAST_ALLOCATED;
+
+public:
+    void jettison(PassOwnPtr<CodeBlock>);
+    void clearMarks() { }
+    void mark(void*) { }
+    void deleteUnmarkedJettisonedCodeBlocks() { }
+    void traceMarkedCodeBlocks(SlotVisitor&) { }
+};
+#endif
+
+} // namespace JSC
+
+#endif